1. Field of the Invention
The present invention relates to a valve timing controller for controlling operation timing of intake valves or exhaust valves of an internal combustion engine.
2. Description of the Related Art
A conventional valve timing controller for an internal combustion engine, which adjusts a phase angle of a camshaft with respect to a crankshaft of the internal combustion engine to adjust open and close timing of the intake valves or exhaust valves, includes a variable valve timing mechanism for adjusting a rotational phase of the camshaft to adjust the valve timing.
The variable valve timing mechanism regulates the duty value of the current passing through a linear solenoid valve for controlling oil pressure to adjust the rotational phase so that the valve timing can be quickly displaced to the most advanced angle side and power consumption required to hold the valve timing at the most advanced angle side can be reduced.
Further, a time period Y during which a 100% ON duty value is output is determined based on the deviation ΔTA of the target value TA of the rotational phase, which is in accordance with the operation conditions, the temperature of oil, and the power supply voltage, when the target value TA is switched to the most advanced angle side that is a stopper position, and the 100% ON duty value is output to the linear solenoid valve during the time period Y since the time when the target value TA is switched to the most advanced angle side. After the time period Y passes, a duty value X required to hold the valve timing at the most advanced angle side is determined in accordance with the power supply voltage at a given time, and the 100% ON duty value is reduced to the determined duty value X, to thereby hold the valve timing at the most advanced angle side (see, for example, Japanese Patent No. 3337396).
The conventional valve timing controller for the internal combustion engine is, however, configured to output the driving duty value provided to the linear solenoid for controlling the rotational phase of the camshaft at the maximum value (100%) when the target value TA of the rotational phase of the camshaft is switched to the most advanced angle position acting as the stopper position, and to then output the duty value X, with which the most advanced angle position is held, when a predetermined duration of time (Y) is passed after the target value TA is switched to the most advanced angle position. Consequently, the power consumption is increased since the overcurrent is provided to the linear solenoid in order to hold the rotational phase angle of the camshaft at the most advanced angle position.
Further, the conventional valve timing controller for the internal combustion engine is also configured to, when the target value TA of the rotational phase of the camshaft is switched to the most advanced angle position acting as the stopper position, output the driving duty value provided to the linear solenoid at the maximum value (100%) and the valve timing controller is struck to the stopper position at the maximum striking speed. Consequently, there is a problem that it may be difficult to ensure durability of the stopper of the variable valve timing mechanism when the rotational phase is frequently adjusted to the most advanced angle position acting as the stopper position.